A method of this kind is generally known. It is used, for example, for the recognition of dangerous delays or of rolling or roll-over movements of the vehicle in order to be able to initiate suitable safety measures, as required, e.g. the tightening of seat belts, the triggering of airbags and/or the deploying of a roll-over bar or of a reinforced neck support.
A vehicle delay is typically determined by an acceleration sensor which monitors the acceleration of the vehicle in the direction of travel. The angular speed of the vehicle about its longitudinal axis and the lateral and vertical acceleration of the vehicle are usually measured for the determination of the rolling or rollover movement. The angle of roll or of rotation of the vehicle is determined by a numeric integration of the rolling rate or of the angular speed and is optionally corrected by the measured acceleration values in the lateral or vertical direction.
Typical rolling or rollover movements such as a rolling movement of a motor vehicle over a crash barrier or down an embankment take place comparatively slowly. The angle of roll of the motor vehicle in such cases usually increases from 0° to 90° in approximately 1 to 2 seconds, i.e. the vehicle tilts from a normal road holding position onto the side in 1 to 2 seconds. Since there is a comparatively low risk of head injury to the vehicle occupants with such a slow rolling movement, a detection time of approximately 600 to 700 ms, which corresponds to an angle of roll of approximately 30° to 40°, is sufficient in order, for example, to activate a rollover bar or an airbag.
However, faster rolling movements or rollover movements such as can occur on sand contact, i.e. on an at least partial skidding of the vehicle off a paved road, or on a contact of the vehicle with a curb, have proved to be problematic. For the effective avoidance of injuries to the vehicle occupants, a reliable detection of the rotational movement is already desirable in such cases on a tilting of the vehicle by less than 10°. This requires a fast detection of the rolling or rollover movement in the range of less than 300 ms.
To achieve such a fast detection time in the known method described above, the detection time can, however, not easily be reduced from 600 ms to 700 ms to less than 300 ms, since such a measure would increase the sensitivity of the method by so much that also such rotational movements of the vehicle would be recognized as rolling or rollover movements which are in reality not rolling or rollover movements at all.
The reason for this is that the rotation parameters such as the angle of roll or the angular speed of a tilting movement of a vehicle, which do not result in a roll-over, do not differ substantially in the course of the first 250 ms to 350 ms from those of a tilting movement which ultimately ends in a roll-over of the vehicle. Safety measures could therefore be initiated unnecessarily under certain circumstances.